文本框内默认有提示字符串，鼠标点击后，提示消失

//文本框内默认有提示，鼠标点击后，提示消失

using UnityEngine;
using System.Collections;

public class BH: MonoBehaviour {
    string stringToEdit="stringToEdit";
    // Use this for initialization
    void Start () {

    }
    // Update is called once per frame
    void Update () {
        if(GUI.GetNameOfFocusedControl()== "XXX"&&stringToEdit=="stringToEdit")
        {
            stringToEdit="";
        }
        if(GUI.GetNameOfFocusedControl()!= "XXX"&&stringToEdit=="")
        {
            print(GUI.GetNameOfFocusedControl());
            stringToEdit="stringToEdit";
        }

    }
    void OnGUI(){
        GUI.SetNextControlName("XXX");
        stringToEdit = GUI.TextField (new Rect (10, 10, 200, 20), stringToEdit, 25);
        GUI.TextField(new Rect (10, 50, 200, 20),"");
    }
}